1. Field of the Invention
The present invention relates to a structural design for lithium ion cells. More specifically, this invention is directed to a structural design for a cell feed-through arrangement that permits a high torque on the cell terminal post connection, wherein the feed-through has a very low impedance, volume and weight, presents excellent thermal shock properties and is hermetic to moisture.
2. Background of the Related Art
Lithium ion cells are used frequently in many of today""s products. They are used in a wide variety of consumer and industrial products. As with any type of battery, the use life of the cells is extremely important. Through the years, technology has increased the use life of all types of batteries by making the batteries more durable. Batteries have become more durable because their designs have gotten better. Therefore, battery cells that have been designed to be more durable consequently increase the use life of the battery. Designing a more durable cell continues to be a goal of battery producers everywhere.
A major problem that occurs that affects the durability of a battery is the breakdown of the seals that are necessary to keep electrolyte within the battery. Seals can breakdown or be damaged for many reasons, some of which include moisture, thermal-shock and shear torque between the seal and its adjacent component. If damage to the seal can be prevented, then the durability of the battery can be increased thereby increasing the life of the battery. The design of the battery is directly related to the damage that is cause to the seals.
Problems occur when the design of the battery is such that the feed-through is directly connected to the external terminal of the battery. A feed-through, sometimes referred to as a pass-through, is a xe2x80x9cholexe2x80x9d in the cell housing that allows the external terminal of the battery to pass through the cell housing to be in contact with the electrolyte within the battery. These xe2x80x9cholesxe2x80x9d, or feed-throughs, are slightly larger than the external terminal of the battery. This size difference creates a gap in the feed-through between the terminal and the cell housing. This gap is filled through the use of a seal. Therefore, in the conventional battery, the seal is in direct contact with the external terminal of the battery.
When the seal is in direct contact with the external terminal of the battery, any torque applied to the external terminal is applied directly to the feed-through and to the feed-through""s seal. This torque applied to the seal causes damage to the seal thereby reducing the life of the battery.
Along with the physical design of the battery, the type of seal that is used in the feed-through affects the durability and consequently the life of the battery. Batteries are subjected to many various types of environments. If any of the environments to which the battery is exposed contains contaminants or moisture, the seal becomes extremely important. The seal acts as a protective barrier. It serves to prevent any of the contaminants or moisture from reaching the interior of the cell. In order to properly accomplish this, the seal itself must be impermeable to moisture and must maintain its integrity in the face of thermal-shock. The conventional mechanical seals are moisture permeable and do not readily maintain their integrity in the face of thermal-shock.
The present invention is directed to a structural design for a cell feed-through that permits a high torque on the cell terminal post connection, wherein the feed-through has a very low impedance, volume and weight, presents an excellent thermal shock properties, and is hermetic to moisture.
An object of the present invention is to provide a battery cell designed to minimize the torque on the feed-through seal that results from torque applied to the external terminal.
It is another object of the present invention to provide a battery cell designed to extend the life and durability of the battery.
It is still another object of the present invention to provide feed-throughs with very low impedance, volume and weight.
It is yet another object of the present invention to provide feed-throughs with excellent thermal shock properties.
It is still another object of the present invention to provide feed-throughs that are hermetic to moisture and other impurities.
The present invention achieves the first of the above objects by providing a plurality of pass-throughs, each having its own seal, which are connected to a terminal plate to which the terminal post is connected. That is, the terminal post does not pass directly through the cell housing and, therefore, does not transfer torque directly to the seals. Instead, the plurality of pass-throughs off-set the shear torque load from a single locationxe2x80x94i.e., the terminal post as in the conventional designxe2x80x94to a distributed compression load on two or more locations. Because the seals are thus not torqued, but are compressed instead, they are not as easily damaged.
That is, each pass-through includes an anchor portion which is attached to the inside of the cell housing by, for example, welding or by heating the housing to expand the xe2x80x9cholesxe2x80x9d and dropping the pass-through into position. A post member passes through the anchor portion, and is connected to the terminal plate as well as to the electrodes within the cell. An insulating seal is then disposed between the anchor portion and the post member. Thus, when the terminal post is torqued, a compression force is placed on the insulating seals. This arrangement provides an insulating seal which maintains its integrity in the face of torque on the terminal post.
The present invention achieves the remaining objects by providing a glass-metal pass-through. That is, the insulating seal is hermetically sealed to the metal post member and to the metal anchor portion. Therefore, the seal is not moisture permeable and, therefore, does not allow contaminants to enter the cell housing.